Trench metal oxide semiconductor (MOS) transistors have been used as power transistors for switching external loads. Trench MOS transistors are one type of power transistor that exhibits electromagnetic susceptibility (EMS). EMS quantifies the immunity of a transistor switch to noise. If the transistor has a poor EMS, it may incorrectly switch from an off state to an on state in response to noise. This can be problematic in a noisy environment.
In one prior device, the power transistor had a gate switchably coupled through a resistor to a source. The gate and source were connected by the switch when it was desired to keep the power transistor in an off state. Since the gate and source were connected, the voltage between them was minimal, and the power transistor remained off. The switch was open when it was desired to allow the power transistor to be in an on state as controlled by a difference between the gate voltage and source voltage.